In concert with the current demand for electronic equipment of smaller size and more multi-functions, the interconnection technology of printed circuit boards and semiconductor packages seeks for a higher density and further miniaturization. As a result, adhesives and adhesive films are required to have sufficiently high heat resistance and low modulus to accommodate the high-temperature process during mounting and relieve thermal stresses upon installation of electronic parts.
In the prior art, low modulus materials were developed by introducing siloxane structures into polyimides and polyamide-imides which are heat resistant resins. These siloxane-modified polyamide-imides are disclosed in JP-A 5-009254 and JP-A 6-116517. However, these resins are less adherent to copper foil and less heat resistant.
JP-A 10-060111 and JP-A 6-271673 discloses to blend a siloxane-modified polyamide-imide with a compound having at least two maleimide groups for improving high-temperature properties. This resin composition is less adherent, especially to copper foil. Japanese Patent No. 3,221,756 corresponding to U.S. Pat. No. 5,677,393 discloses a heat resistant adhesive film comprising a polyimide silicone having phenolic hydroxyl groups and an epoxy resin. Since the phenolic hydroxyl groups are located at sterically dense positions and thus hindered from reacting with the epoxy resin, the bonding effect of hydroxyl groups that arises from the reaction of phenolic hydroxyl groups with the epoxy resin is not expectable.